The present invention generally relates to a dental post and core system for endodontically-treated teeth. More specifically, this invention relates to a passive dental post and core system having a flexible inelastic post, wherein the post is made from a material having a plurality of distributed fibers, such as, for example, medical grade optical fibers, other medical grade fibers or other fiberglass materials, which are held together in a matrix in a resin, such as a polyester resin or a vinyl ester resin.
In the preferred embodiment, the flexible post has a modulus of elasticity less than or equal to that of tooth dentin, to prevent widespread damage to a tooth in a traumatic event, when a conventional post would flex less than the tooth dentin, causing tooth fracturing where the flexible dentin violently contacts the inflexible conventional post.
Also in the preferred embodiment, the endodontic post of the present invention is cylindrical, rather than wedge shaped as in many non-metallic posts, because of its less stressful impact and its decreased wedging effect, which can cause immediate and/or residual root fractures.
While the fibers may be axially aligned, preferably at least one of the fibers extends non-axially aligned with respect to a straight axis extending from the apical end to the opposite coronal end of a root of a tooth.
In one embodiment, the present invention includes an endodontic dental reinforcement post for endodontic and reconstructive pin therapy comprising a prefabricated bundle of loosely compacted fibers in a cured resin, with the post extending from an apical end to a coronal end of a tooth canal.
For example, the fibers may be a bundle of fibers, a longitudinally twisted bundle, a twisted braid, a woven lattice, a helically wrapped bundle of fibers, or a composite of randomly dispersed fibers in a binder.
In this preferred embodiment, at least one of the fibers extends non-axially aligned with respect to the straight axis of a root of a tooth.
For example, in a bundle of fibers, while some of the fibers may extend parallel to the straight axis of the root, at least one or more of the fibers extend in an axial direction which is not parallel to the straight axis of a root of a tooth. That is, at least one or more of the fibers extends in a transverse or angled direction away from the straight axis of the root of a tooth.
With respect to a longitudinally twisted bundle, a twisted braid, a helically wrapped bundle of fibers, the twisting or helical wrap of the fibers causes many, but not necessarily all, of the fibers to extend non-axially. Concerning a woven lattice of fibers, while one set of fibers could extend axially parallel to the straight axis of the root, the other intersecting set of fibers extends in a direction which is non-axially aligned with respect to the straight axis of the root. Even if most of the weft of a weave of a plurality of fibers extends parallel to the straight axis of the root, at least one or more fibers constituting the warp of the weave of fibers extends non-axially with respect to the straight axis of the root of the tooth.
Moreover, concerning a composite of randomly dispersed fibers, there is always the possibility of one or more of the fibers being axially aligned to the straight axis of the root of a tooth. However, in order to be randomly dispersed, at least one or more of the fibers extends non-axially with respect to the straight axis of the root of a tooth.
Preferably, the post is radio-opaque and bears a color simulating that of a natural tooth.
Rigid dental post and core systems are widely utilized to restore endodontically-treated teeth. Post and core restorations are routinely used to create an adequate foundation for the final restorative step, which may be a crown, inlay, or a fixed partial denture abutment. Generally, a post is provided for retention and lateral stability of the restoration. The core provides support for the crown. Two general types of post and core systems are known in the art: xe2x80x9cactivexe2x80x9d or screw-in type systems and xe2x80x9cpassivexe2x80x9d type systems. Active post and core systems mechanically engage the walls of the root canal and tooth dentin. Passive post and core systems are bonded in endodontically treated teeth utilizing cements and the like.
Two major problems are encountered when restoring an endodontically-treated tooth. Firstly, the tooth is more susceptible to fracture, and secondly, there is generally less coronal structure with which to work. The greater susceptibility of a tooth to fracture after endodontia may result from the tooth being more brittle. However, studies of the changing mechanical properties of pulpless teeth do not generally support this theory equating dryness with reduced mechanical strength. It appears that the greater susceptibility for fracture in an endodontically-treated tooth results from mechanical weakening of the tooth during root canal therapy and refinement of the root canal. Improvements in restoration techniques that reduce mechanical weakening are therefore desirous.
An endodontically-treated tooth is generally severely compromised either due to trauma or neglect. Thus, traumatic fractures, removal of old restorations and carious tissue, and preparation of root canal access may not leave enough tooth to maintain the xe2x80x9cdome effectxe2x80x9d of the tooth or to retain a crown.
The stress concentrations in a tooth resulting from the rigid post and core systems of the prior art also play a vital role in tooth fracture. Stress concentrations can be impacted through system design and/or restoration techniques. Various studies and investigations into the susceptibility of endodontically-treated teeth to fracture and the contribution of rigid dental post and core systems to such fracture have been conducted. xe2x80x9cA Comparison of Intracanal Stresses in a Post Restored Tooth Utilizing the Finite Element Methodxe2x80x9d, Cailleteau, Johnny G., Rieger, Monty R. and Akin, J. Ed, Journal of Endodontics, Vol. 18, No. 11, November 1992, pp. 540-544, reports that placement of a rigid post within a tooth alters the pattern of stress along the root canal as compared with an intact tooth. Instead of strengthening the tooth the post stiffens the coronal posted section and shifts the flexure point apically. The effect of this stiffening causes the non-posted apical portion of the tooth to deform at the post apex, resulting in a stress increase in that portion of the canal wall. Also, the cyclic loading and unloading of an incisor during mastication requires consideration of fatigue failure. Since the maximum bending stresses occur in connection with the apex of the post, any inclusions or defects within the wall of the dentin near the apical end of the post would create stress concentrations that increase the risk of a fatigue crack formation. Defects and microfractures introduced during endodontic treatment and post access preparation could become areas contributing to stress concentrations. Studies have also shown that more intact tooth structure provides better resistance to fracture than a metallic post. There is also evidence that stresses in the tooth tend to increase as the post diameter increases.
A flexible post eliminates these problems and a cylindrical flexible post performs even better. A post and core system utilizing a flexible post shifts the stress concentrations coronally, eliminates the introduction of defects during post access preparation and post placement, and leaves more of the tooth intact.
The main function of a post is to provide retention to the core. Relieved of its expectation to facilitate resistance to tooth fracture, the post can be designed to optimize its retentive properties. Several factors govern the retentiveness of endodontic posts. The shape of the post and its length are among the essential factors.
For example, unlike the preferably flexible cylindrical post of the present invention, tapered dowels have been found to be significantly less retentive than parallel-sided posts. While inflexible metallic posts are generally cylindrical and/or threaded, non-metallic resin-based posts are generally tapered, such as described in French Patent Publication No. 8,515,527 of Barbe et al, published Apr. 10, 1987 or U.S. Pat. No. 5,326,263 of Weissman, where a tapered cylinder is seated within a wide tapered resin base. Such tapering was believed to enhance removal of a first temporary post to be replaced by a permanent post. Weissman ""263, also describes a temporary flexible post including a single fiber optic cable rod, which is removed from a reamed, wedged shaped drilled out tooth canal before installation of a permanent, inflexible post. The post of Weissman ""263 also has the drawback of being smooth on its surface, to facilitate easy removal of the temporary post.
Weissman ""263 also describes a flexible tapered post insertable within a converging, tapered, canal wherein the converging tapered canal is filled with a curable composite. It lacks any texturization of the surface, which helps to maintain a permanent post in position within a tooth canal.
U.S. Pat. No. 5,165,893 of Thompson discloses using a fiber optical plunger applicator to apply a liner adjacent to the inner surfaces of a root canal. It does not describe a permanent post as in the present invention.
A serrated 5.5-mm parallel-sided dowel was found more retentive than an 8-mm tapered post. Tapered posts, such as described in Barbe noted above, provide high shoulder stresses but have an undesirable wedging effect. The wedging effect results in part from the prior art placement of a straight rigid post in a naturally curved and varying diameter root canal.
Furthermore, active threaded posts are very retentive, but may impose too much stress on the tooth, especially compromised teeth.
Thus it appears that a flexible passive, textured, parallel-sided cylindrical post is a preferred structure for dental post and core systems. A flexible, passive, textured parallel-sided cylindrical post provides the previously-mentioned advantages in preventing tooth fracture and additionally permits the post to extend for a greater length into the root canal for improved retention.
In addition to post shape and length, adequate retention is a function of cementing mechanisms. Various cementing medium have been studied. Utilization of low viscosity resin cement in combination with smear layer removal can be considered a universal post cementation technique. In addition to good retention, this cementing technique offers the benefits of a cement with very little resistance to post insertion, thereby minimizing stresses applied to tooth structure during cementation. However, the invention of the present disclosure is not limited by the cementing process used.
Nevertheless, light sensitive cements, such as REVOLUTION(copyright), of E.N.D. Dental Products Company, Somerset, N.J., can only act when used with a translucent substance. Therefore, there is a need for a translucent endodontic post as well.
A major problem of dental posts for endodontic root canal therapy is the inelasticity of posts, even if partially flexible. For example, stainless steel posts have a GPa (giga Pascals) of approximately 190, and titanium posts have a GPa of approximately 100, wherein the higher the GPa number the less elasticity of the post. One attempt to solve this problem is a non-metallic, carbon fiber, unidirectional post known commercially as C-POST(copyright) of Bisco Company of Itasca, Ill.
However, its modulus of elasticity is approximately 21, as reported in product literature therefor, whereas natural tooth dentin has a lower modulus of elasticity of 18. Since the modulus of elasticity of the C-POST(copyright) exceeds the modulus of elasticity of natural tooth dentin in which the C-POST(copyright) is inserted, the C-POST(copyright) may cause a tooth to fracture because the C-POST(copyright) is less elastic than natural tooth dentin.
Therefore, there is an unsolved need for an endodontic post for root canal therapy wherein the post has a modulus of elasticity less than that of natural tooth dentin. As a result, such a post would have less a likelihood of fracture, and will reduce the need for subsequent re-doing of post and core therapy after a post fractures or extraction of any non-restorable teeth.
Other background art includes an elastic, wire pin having a plurality of flexible, radially extending fins along its length, as is disclosed in German Patent No. DE 3,643,219 to Weisskircher. While providing some advantages over the prior art rigid post, the xe2x80x9chigh degree of elasticityxe2x80x9d of the Weisskircher pin will cause it to try and retain its initial shape in the root canal. During and after placement, flexing of the pin will cause the apical end of the pin to lay against the wall of the root canal. Stress concentrations in the tooth as known for rigid posts will thereby be induced. A pin formed from wire also has low retention characteristics and tends to rotate within the root canal. Radial fins are utilized in the Weisskircher disclosure to resist rotation of the wire pin. However, these radial fins may become further sources of stress concentrations and fatigue failure as the wire pin rotates. No prior art known to the present Applicants discloses or suggests a flexible post in a dental post and core system that is flexible and inelastic, i.e., that conforms to the shape of the root canal to eliminate the stress concentrations that facilitate tooth fracture.
Furthermore, U.S. Pat. No. 4,778,389 to Salvo discloses a dental post construction to eliminate lateral stress in a tooth wherein a rigid, split post is formed by parallel sections joined at a marginal top portion of the post head.
U.S. Pat. No. 5,073,112 to Weil discloses a dental post having an active portion and a passive portion. It also describes a combination sleeve and threaded post, wherein part of the post is threaded, and part is not threaded. A temporary light transmitting rod is inserted to provide light to a light activated composite cement.
U.S. Pat. No. 5,074,792 to Bernadat discloses a passive post and core system comprising a rigid peg disposed in a porous sheath formed of high-strength filaments, wherein the peg has a set of parallel radially extending fins extending from the peg. The filaments in Bernadat are found in the sheath surrounding the peg, not in the peg itself.
U.S. Pat. No. 732,922 of Clark describes a pin for teeth which is flexible, but only by virtue of the fact that the pin includes a base and two tapered pins extending from the base, with a space therebetween, so that the tapered pins can close toward each other within the space.
U.S. Pat. No. 4,952,150 of Schiwiora discloses a tooth root post which includes a tip of solid flexible metal or metal alloys. In contrast to Schiwiora ""150, in the present invention, the root post is made of a plurality of metallic or non-metallic fibers, as opposed to a solid piece of metal.
U.S. Pat. No. 4,934,936 of Miller describes a serrated dental post. U.S. Pat. Nos. 622,670 of Dwight and 1,218,289 of Maker both disclose solid threaded posts with a core spacer neck extending therearound.
International Search Publication No. WO 91/07142 (PCT/FR90/00831) to Reynaud et al., which also issued as U.S. Pat. No. 5,328,372, discloses a dental post and core system having a post formed from equally-tensioned fibers of composite material. In Reynaud, the fibers of the composite material are all laid axially within the post and embedded within a resin. Because the fibers are equally tensioned and extend only axially aligned and continuous, any modification of the post in Reynaud may cause a major spreading, continuous, fault line crack in the resin of the post, thus losing integrity of the Reynaud post.
In contrast to Reynaud ""372, as noted hereinafter, in the present invention the fibers are loosely compacted and cured in a resin, and not pre-tensioned and stretched under tension by traction, as required in Reynaud et al, as noted in the specification therein.
In further contrast to Reynaud et al, preferably at least one or more of the fibers extends in a direction which is non-axially aligned with respect to the straight axis extending from the apical end to the opposite coronal end of a root of a tooth. Because there is a plurality of directions with respect to the fibers, such as at least one fiber running non-axially, the possibility of a spreading, continuous fault line crack is significantly reduced, thereby achieving unexpected beneficial results not suggested in Reynaud ""372. Also, while the Reynaud ""372 post can be cut in length, it is contraindicated to shave or adjust the Reynaud ""372 post in all directions so that the possibility exists of causing the carbon rods to develop axial fault crack lines.
Other background art includes U.S. Pat. No. 4,936,776 to Kwiatkowski, which discloses a translucent post and core structure to minimize gingival discoloration adjacent a dental restoration, and U.S. Pat. No. 3,949,476 to Kahn discloses a xe2x80x9cdirectxe2x80x9d method of restoring an abraded or broken tooth.
Soviet Union Patent No. SU 1,457,914 of Feb. 15, 1989, to Stomatology Research Institute discloses a method of making a pin stump insert. Moreover, Soviet Union Patent no. SU 1,519,684 of Nov. 7, 1989 describes a threaded grooved tooth implant. Furthermore, Soviet Union Patent no. SU 1,277,950 of Dec. 23, 1986 discloses an electrochemical bonding procedure for coating dental pins.
West German Patent No. 1,541,209 to Kurer discloses the now conventional threaded, screw-in type active post.
U.S. Pat. No. 4,622,012 of Smoler describes a two part dental post system with an outer hollow sleeve post and an inner post insertable within the outer post.
U.S. Pat. No. 4,759,718 of Szeguary describes an active threaded post. U.S. Pat. No. 4,726,770 of Kurer, Swiss Patent No. CH669514 of Polydent, U.S. Pat. No. 4,696,646 of Maitland, and U.S. Pat. No. 4,631,030 of von Weissenfluh, all describe interproximal contact wedge tools for filling cavities in a tooth.
U.S. Pat. No. 5,088,927 of Lee describes a dental plastic member impregnated with metal to enhance x-ray pictures. U.S. Pat. No. 5,030,093 of Mitnick discloses a dental restoration apparatus including a material setting tool which includes an optical probe. U.S. Pat. No. 5,092,773 of Levy describes an apparatus for filling the apex of a root canal with a laser mettable material. U.S. Pat. No. 5,116,227 of Levy describes a laser operable canal forming tool.
French patent application no. FR 2,645,431 of Levy describes a laser tool for cleaning a root canal.
German Patent no. DE 3,411,366 of Neumeyer describes an optical probe for periodental treatment.
U.S. Pat. No. 4,684,555 of Neumeyer describes dental retention pins made of metal, plastic, porcelain or ceramics. However, Neumeyer ""555 includes two layers, an inner layer and an outer coating layer. This is in contrast to the present invention, in which there is an even distribution of fibers through the endodontic post. As a result, the post of the present invention requires no outer bond assisting or enhancing layer, as is needed in Neumeyer ""555. Furthermore, Neumeyer ""555 is not concerned with providing a pin having a modulus of elasticity less than tooth dentin, as is the endodontic post of the present invention.
Other prior art includes U.S. Pat. No. 4,645,457 of Goldman which describes a method of cleaning a root canal prior to installation of a post therein and U.S. Pat. Nos. 4,990,090 and 5,145,373, both of Roane, which describe grooved and/or threaded endodontic posts.
U.S. Pat. No. 5,320,530 of Fong describes an endodontic apparatus for retrofill cavity preparation and U.S. Pat. No. 4,172,867 of Devault describes an index pin and die spacer combination for dental use.
Furthermore, U.S. Pat. No. 5,407,973 of Hasegawa describes a dental cold-polymerizing resin composition and U.S. Pat. No. 5,284,443 of Weil describes a method of inserting a removable light transmitting mandrel point temporarily within a deposit curable composite material, wherein the light transmitting member provides light to cure the material.
In addition, U.S. Pat. No. 5,007,837 of Werly describes a method of filling a cavity and U.S. Pat. No. 822,582 of Carmichael describes an attachment for natural teeth and method of forming the same. U.S. Pat. No. 4,778,388 of Yuda et al describes root canal posts.
European patent application publication no. 0076086 of Carse dated Apr. 6, 1983, describes a threaded dental pin having a threaded pin member and a synthetic resin having a sharing neck 18.
British Patent no. 1,302,022 of Technical Dental Developments dated Jan. 4, 1993 describes an improved dental crown which uses resin with metal particles for casting a crown. It is not for a permanent post.
French Patent publication no. 2,626,167 of Himmel assigned to Compodent Research and Applications Ltd., dated Jul. 28, 1989, also known as British Patent no. GB 2,214,087, describes a dental post pin and a method of making the pin. The dental post pin essentially includes a central filament of yarn which is axially aligned within a sheath of fiber containing resin. Himmel also describes a plastic, ceramic, carbon or glass central wick or filament surrounded by an outer sheath of resin which could have other fibers in it.
In contrast, in the present invention, the fiber bundles preferably are equally dispersed throughout the peg of deposit and are not limited to the central portion. Also, in the present invention, there is no differential of an outer sheath having denser fibers from the loosely packed fibers of the central core.
French Patent publication no. 2,587,197 of Reynaud dated Mar. 30, 1987, and U.S. Pat. No. 4,738,616, also of Reynaud, describe dental posts which are made up of a serial of conical parts that are joined together in a cylindrical conical fashion.
German patent no. DE 3,825,601 of Strobl dated Aug. 9, 1989, describes a dental reconstruction post for endodontics, wherein a fiber reinforced plastic is used. However, there is no mention of the need for imparting flexibility in the post. In Strobl, the fibers are used specifically to strengthen the post and increase rigidity, not to make the post more flexible, as in the post of the present invention.
For example, in paragraph 3 of the section of the patent application of Strobl entitled xe2x80x9cState of Technology, with Sourcesxe2x80x9d, it is stated that the strength and rigidity of plastics can be increased significantly by incorporating high-strength fibers with a high modulus of elasticity.
In contrast, the endodontic post of the present invention has a low modulus of elasticity, and is thus flexible.
Furthermore, Strobl teaches a wedge shaped post, which increases wedging stress within the tooth. While Strobl discloses rigid, diagonally extending non-axially fibers in the crown stump attached a post, in the post itself the fibers are described as lying in the direction of the root pin, i.e. axially, unlike the preferred embodiment of the present invention.
French Patent publication no. 1,457,914 of Badische dated Dec. 8, 1965, describes a thermal plastic material.
Currently-marketed dental post and core systems such as the FLEXI-POST(copyright); the DENTATUS POST(copyright), the RADIX POST(copyright) and the BRASSELEAR(copyright) screw posts all advocate screwing threaded rigid posts into straight paths machined into the tooth dentin. These present day posts are also generally formed from rigid metals such as steel, titanium and other alloys which do not flex in the same manner as a natural tooth. As noted before, this differential in flexibility between the natural tooth and the post may cause tooth fracture when the restored tooth is stressed during mastication or from trauma. These cast posts are subject to the same limitations and require an additional laboratory fee and an additional visit to the dentist to complete the procedure.
A means to quickly and easily identify the components of a post and core system is also needed in the prior art. Presently, there is either no color-coding of post and core systems or the color identification consists of an inconspicuous dot of color. Brightly-colored means of identifying post and core systems would significantly advance the art. The lack of a color protocol in the prior art creates confusion, eye strain and a sloppy work environment. The inability to readily identify each post and core by sight creates problems before, during and after the procedure is completed. Firstly, before the procedure is initiated the dentist and staff must select the post and core and isolate it from others that may be very close in size. During the procedure the dentist must carefully avoid confusing the selected post and core. After the procedure the used and unused devices must be readily identified for contamination control. Further, a post and core system installed by one dentist may later require an emergency or other procedure by a different dentist in a completely different part of the world. Color-coded identification would eliminate uncertainty and guesswork.
The post and core system of the present invention overcomes all of these limitations of the prior art.
A primary object of the present invention is therefore to provide a flexible, inelastic dental endodontic post with a modulus of elasticity less than natural tooth desin.
Another object of this invention is to provide a passive and bondable dental post and core system for endodontically-treated teeth.
Yet, another object of this invention is to provide a dental post and core system that reduces the susceptibility for tooth fracture in endontically-treated teeth.
A further object of this invention is to provide a method for restoring endodontically-treated teeth that reduces the susceptibility for tooth fracture.
Another object of the present invention is to provide a dental post and core system that reduces the mechanical weakening of tooth structure by relieving stress concentrations.
Another object of the present invention is to provide a dental post and core system that reduces the risk of a dentist creating perforations and microfractures during post placement.
It is also an object of the present invention to provide a flexible post in a dental post and core system that automatically adjusts to the contours of a root canal during placement.
Another object of this invention is to provide a post and core system having a flexibility that closely mimics the flexibility of the pulp and dentin tissue of a natural tooth.
Another object of the present invention is to provide a dental post and core system that reduces the amount of time required to restore an endodontically-treated tooth.
It is also an object of this invention to provide a dental post and core system that can be safely and quickly installed by any dentist in a single visit.
Another object of this invention is to provide a dental post and core system formed from material that can be readily shaven to accommodate canal irregularities and in-between root canal sizes without loosing its physical properties.
Another object of this invention is to provide a dental post and core system that is radio-opaque.
Another object of this invention is to provide a method of restoring endodontically-treated teeth that eliminates or nearly eliminates drilling for post placement and that can be installed using inexpensive, readily available endodontic drills.
Another object of this invention is to provide a post in a dental post and core system that fits intimately within a root canal and that accepts standard dental cements.
Another object is to provide a color-coded dental post and core system for identification purposes.
A further object of the present invention is to provide dental post and core system that substantially fits all teeth.
It is another object of the present invention to provide a dental post and core system that can be provided in standardized sizes for mass production efficiencies.
A still further object of this invention is to provide a restoration system of flexible dental pins for teeth previously classified as hopeless and difficult, such as hemisected and dilacereted teeth and other conditions of extreme loss of tooth structure.
These and other objects and advantageous of the improved dental post and core system of the present invention will be apparent to those skilled in the art from the following description of preferred embodiments, claims and appended drawings.
In keeping with these objects and others which may become apparent, the present invention is a dental post and core system that includes an inelastic flexible post of a bundle of fibers, such as medical grade optical fibers or other fiberglass fibers held together in a resin, such as a polyester resin or a vinyl ester resin.
In contrast to Reynaud ""372 in the present invention the fibers are loosely compacted and cured in a resin, and not a pre-tensioned and stretched under tension by traction, as required in Reynaud ""372, as noted in the specification therein.
The flexible post conforms to the curvature or path of the root canal during placement and reduces mechanical weakening of an endodontically-treated tooth by eliminating stress concentrations at the apical end of the post, by reducing the size of access preparations and by allowing more intact tooth to be retained.
The present invention also provides a method of restoring an endodontically-treated tooth that reduces the time and equipment needed during a procedure and lessens the chance that a dentist will perforate or fracture the canal wall during placement of a post.
The present invention solves the problems of rigid, inflexible inelastic dental posts for endodontic root canal therapy. For example, stainless steel posts have a GPa of approximately 190 and titanium posts have GPa of approximately of 100 wherein the higher the GPa the less elastic is the post. As noted above, the C-POST(copyright) of Bisco Company of Itasca, Ill. is a carbon fiber unidirectional post in an epoxy matrix. However the modulus of elasticity of the C-POST(copyright) is approximately 21 whereas the modulus of elasticity of the natural dentin in a tooth is 18. Since the modulus of elasticity of the C-POST(copyright) exceeds the dentin it is still subject to fractures because it is less elastic than the natural dentin in the tooth itself.
Therefore while the present invention may closely approximate the modulus of elasticity of tooth dentin, in a preferred embodiment the present invention is directed to an endodontic post for root canal therapy wherein the post has a modulus of elasticity which is less than that of natural tooth dentin. As a result there is a less likelihood of fracture of the post, which avoids a complete extraction of the tooth or need for unnecessary surgery.
One embodiment of the present invention includes using medical grade optical fibers of high optical clarity with high pixel counts of between 50 and a 100 thousand, in a twisted bundle of the linearly extending fibers. Another embodiment uses a twisted bundle of other fiberglass fibers.
The purpose of the slow twist in a bundle of the fibers is as noted in Applicants"" prior patent applications, wherein fracture of dental posts can be reduced by removing axial orientation of the fibers in one direction such as in Reynaud or in the C-POST(copyright) of Bisco.
The medical grade fiber optic fibers are traditionally used in optical cables which are normally used in the human body for endoscopic visual examination of internal organs through a tube through which the fibers extend.
In this embodiment, the posts of the present invention are made of silica-based fibers, bundled together, having a pure silica core of SiO2. An example of the silica based fibers are medical grade optical fibers from Polymicro Technologies Inc. of Phoenix, Ariz.
The coating of each fiber is a polymer, such as KYNAR(copyright) (polyvinylidene fluoride) brand resin, or other resins, such as a polyimide, to impart flexibility to the glass fibers. The coating preferably is chemically or mechanically stripped, so it pulls light out transversally through the stripped apertures along edge of the post. This is beneficial when using a light sensitive adhesive which reacts to light. Typical light activating dental cement in the root, which is adjacent to the posts, include REVOLUTION(copyright) bonding light cement of END Dental Products Company of Somerset, N.J. Other non-light activating dental cements include chemical resins, such as SCOTCH BOND(copyright) of 3M Corporation of Saint Paul, Minn., or vinyl ester resins.
In the preferable embodiment the silica-based post fibers are coated with PVDF resin which meets USP class VI pharmaceutical standards. Such a resin is known commercially as KYNAR(copyright) (polyvinylidene fluoride). KYNAR(copyright) (polyvinylidene fluoride) fluoro-polymers are strong, as reflected by their tensile properties and impact strength. They have an excellent resistance to fatigue. However, they are useful in endodontic posts since they are flexible and light transmitting, and they are resistant to mechanical stresses. According to ASTM test D638 they have tensile strength of 5,000 to 6,500 psi yield. They have a tensile modulus according to ASTM test D882 of 150 to 200xc3x97103 psi.
Moreover, the crystalline state of the KYNAR(copyright) (polyvinylidene fluoride) brand resins can be modified in rapid cooling to promote smaller crystalline size with increased crystallinity of their higher values for yield strengths. The KYNAR(copyright) (polyvinylidene fluoride) polymer and KYNAR(copyright) (polyvinylidene fluoride) flex co-polymer grades are in compliance with U.S. Pharmacopia (USP) classification VI.
In an alternate embodiment, E-glass fiberglass fibers are used as a substitute for the silica optical fibers. E-glass is commonly used in the electronics industry; a typical composition is 55% SiO2, 16% CaO, 15% A1203, 10% B203 and 4% MgO. This composition can be altered to achieve preferred properties for this application as described above.
While other size fibers may be used, a typical fiber of the group making up the bundle of fibers, is one thousandth of an inch in diameter. Therefore, a bundle of two hundred fibers has a diameter of approximately 0.05 inch. The final post peg may therefore be also 0.05 inch in diameter, including approximately 200 fibers plus the saturation of the epoxy binder with an optional colorant/opaquer mixed into the epoxy resin to modify and change these properties.
As an alternative to adding an opaquer mix into the epoxy resin, one or more metal fibers or wires at or near the center of the fiber bundle can be used. This would have the added advantage of providing a ready means to remove the post (if this were necessary) by the following method. The single centrally located wire or fiber can be pulled out leaving a pilot hole for guidance of a reamer to facilitate removal.
A preferred embodiment for an epoxy resin in MASTER BOND(copyright) Polymer System EP21LV of Master Bond, Inc. of Hackensack, N.J. MASTER BOND(copyright) is a two component, low viscosity epoxy resin in which the fibers are cast. The rigidity of MASTER BOND(copyright) can be adjusted by adjusting the mix ratio of the two components. Other useful resins include polyester resins or vinyl ester resins. Depending upon the adjustment of the epoxy resin, the number of fibers can vary.
Preferably the bundle of fibers have a rounded end and may also have a tapered end with an optional continuous groove or facet of 50 to 100 micron depths to increase |surface texturing. The standard length of the post is about ⅝ inch and the standard diameter is about 0.04 inch to 0.05 inch, with an optional taper at the top with xe2x85x9 inch linearly. The texturing may be by a die drawn across linearly or axially of 50 to 100 micron depth or it may be etched with acid or laser lights such as carbon dioxide laser or Yag laser or there may be an outer skin sheath added which is texturized. The individual fibers in one post in bundles are optionally twisted or gathered as they come off a spool.
Optionally the post may be tooth colored by adding barium sulfate to the epoxy resin that holds the bundle of fibers together such as in a medical grade epoxy such as bisGMA.
Among other uses for which the fiber based posts may be used is as a dental cavity reconstructive pin to replace titanium, steel, or gold pins which tend to corrode and which do not have a good modulus of elasticity.
This optional use for the fiber based post is as a reconstructive pin for a tooth with large areas of decay or traumatic damage. Such a tooth may be reconstructed using pins as a lattice scaffolding to stabilize the filling. Most prior art pins are metallic which has colorization problems. Furthermore, the flexible pin of the present invention can be looped around and closed into the tooth wherein the canal is back filled with composite material. The looping helps with retention by exerting a lateral force against the inside of the canal to provide an anti-rotational feature for both the post and the pin, wherein the axially extending surface facet is cut.
Other possible uses of the present invention are for hip prosthesis, finger joint restoration or other types of bone implants, to reduce resorption bone dissolution due to stress or infections.
In summary, while in some embodiments, the modulus of elasticity of each post is above, but close to, that of tooth dentin, the preferred embodiment has a modulus of elasticity which is less than that of the tooth dentin, which is about 18 GPa (giga Pascals).
In contrast to this embodiment of the present invention, in the Weissman ""263 post, the reamer does not require any specialized shape at its end as long as its diameter is essentially the same as the diameter of the posts. The Weissman ""263 posts are easily deformable. Also Weissman ""263 describes a temporary fiber optic rod which is removable from a central channel.
In contrast, the present invention is a permanent, flexible post which has fiberglass fibers, or medical grade optical glass fibers, making it an integrally strong post. The micro filaments of the present invention may be treated by coating to impart flexibility and strength to each fiber. This is not done to add flexibility to the unit post but is done to effect the twisting or other non axial arrangements of the fibers to impart strength to the unit post. This allows it to function as a permanent post in all teeth, not only as a temporary post as in Weissman ""263. Furthermore, the Weissman ""263 post requires a composite cement or encasement, which is polymerized by using a bonding light, whereas the present invention can use either a light activated cement or a chemically cured cement, such as a glass ionomer which requires no photo activation.
Moreover, in the preferred embodiment of the present invention, the post is textured to keep it bonded in the canal, whereas the Weissman ""263 post has a smooth surface to intentionally allow it to be removed because it is a temporary post. It has only been suggested to use the Weissman ""263 post as a permanent post in compromised teeth, because the Weissman ""263 post may lack mechanical properties such as tensile shear and compressive strengths.
In another embodiment of the dental post and core system of the present invention, the post includes a core spacer and a flexible, post reinforcing rod extending apically from the core spacer. The core spacer may be flexible, resilient or otherwise deformable and may be selectively attachable or integrally formed with post reinforcing rod. A core may be selectively attached to the upper portion of the core spacer, integrally formed with the core spacer or built-up to custom specifications.
A further embodiment of the present invention is a mutable flexible post. The mutable post of the present invention comprises a bundle of fibers that may be selectively flared at the coronal aspect to provide a core seat or to provide extra surface area to scaffold a core.